1,720,966 research outputs found
Earth Fault Location in Non-Radial Resonant Grounded Networks – Theory, analysis and methods
No full textA common grounding scheme for medium voltage distribution networks and high voltage sub-transmission networks is the resonance grounding scheme. Resonant grounded networks have few interruptions and a high quality of supply, but an important drawback is the particularly challenging conditions for protection systems and fault location methods during earth faults. Specialized methods are required to detect and locate earth faults, and although many fault location methods have been proposed and developed over several decades, reliable earth fault location remains a challenge. The fault location process can often become a manual process of trial and error, and it may take several hours to successfully locate faults. Earth faults are accompanied by overvoltages which are harmful to components in the network, and permanent faults can lead to insulation failure and additional faults. The classical distribution network is radial in structure, and the conventional fault location methods have also utilized this property. The high voltage sub-transmission network is however meshed, and increased meshing of the medium voltage networks as well alters the conditions for fault location methods. This can create both challenges and new opportunities.
This thesis studies earth fault location in non-radial networks. The research methods used include modelling and analysis of networks using electromagnetic transient software, theoretical analysis and development of novel fault location methods, and laboratory tests conducted using physical relays and network models.
First, the application of transient earth fault relays in non-radial networks is studied. Being the only real alternative in the meshed, subtransmission network, these relays have been used extensively over many years. However, transient earth fault relays have gained a reputation for being unreliable among several network operators, and operators are often reluctant to fully trust the relays’ responses during faults. Understanding how well these relays really work in a non-radial network topology is therefore one important motivation behind the research presented in this thesis. Four different transient earth fault relays are analysed and tested in a laboratory setup with the goal of understanding their fault direction indication in non-radial networks. The results show that the lack of a clear forward/reverse direction combined with their inability to gauge fault distance can lead to inconclusive and contradictory responses in non-radial networks. Furthermore, as relays in different locations can have different operating conditions, it is concluded that each relay in the network should be analysed and set individually, contrary to what several relay manuals indicate. Changes made to the network topology in normal operation can also change the conditions for the relays in the network, so careful planning and analysis in advance is required to ensure selectivity and coverage for all faults. A lack of such planning is identified as the most likely cause of the problems experienced by network operators.
Second, the thesis presents novel fault location methods which contribute to more efficient fault location in non-radial networks. The research contributes to the development of methods aimed at precise distance to fault estimation in closed-ring networks, which are verified with promising results in simulations for both permanent and transient faults. The thesis also presents a method for detection, location and clearing of high impedance earth faults. This method consists of two independent earth fault indicators, one of which can be used to provide continuous fault indication throughout a sectionalizing process. As a result, the method can aid the network operator in narrowing down the estimate of the fault location. Laboratory tests demonstrate the feasibility of the proposed method, but the method’s sensitivity is ultimately limited by the quality of the current measurements. The two earth fault indicators function up to 15–20 kΩ and 50 kΩ in the laboratory, respectively, but further study of real current sensors is required to predict the sensitivity in real networks
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Feeder selection algorithms for high-impedance faults in resonance grounded distribution systems
Get PDFHøyspente distribusjonsnett med spolejording har tradisjonelt sett benyttet den stasjonære Wattmetriske algoritmen til å identifisere avgangen med jordfeil. Likevel har metoden vist seg å være utilstrekkelig, noe som har gitt motivasjon til forskere for å utvikle nye og bedre metoder. Som et resultat av forskningen har QU algoritmen, Directional algoritmen og CPS algoritmen blitt utviklet. Alle tre utnytter transiente verdier. Men med ny teknologi stilles det spørsmål til deres evner og pålitelighet. Og med ulike algoritmiske prosesser vil algoritmene påvirkes ulikt avhengig av systemet og hendelse.
Når en jordfeil oppstår vil systemet tilvenne seg den nye situasjonen med å øke fasespenninger, noe som krever oppladning av avgangene. En sammenheng mellom nullsekvensspenning og den transiente ladningsprosessen i nullsekvensen har tillatt QU algoritmen å identifisere friske og feilbefengte avganger ut ifra deres linearitet. Til motsetning kan Directional algoritmen identifisere avgangene ut ifra dere flyt av energi i nullsekvensen, mens CPS algoritmen akkumulerer multifrekvente admittanser fra fundamentale og harmoniske komponenter for å oppnå identifiseringen.
Med å generere kvantitative resultater fra numerisk simulering, samt gjennomgå induktive slutninger fra tendenser observert, har de forskjellige metodene vist ulikheter ettersom feilmostanden og karakteristikken til den feilbefengte avgangen varierer. Algoritmene har også vist ulikheter avhengig av kompenseringsgrad, andel kabler i nettet og feilfasen i et system som er utsatt for en høy feilmotstand. Valg av algoritme vil deretter påvirke hvor høy feilmotstand retningsbestemmelsen takler, om en feil retningsbestemmelse blir gjort og om de friske avgangene identifiseres. De nye algoritmene vil uansett kunne forbedre retningsbestemmelsen i er spolejordet nett, men ingen er suveren.High voltage distribution systems with resonance grounding traditionally utilize the steady-state Wattmetric algorithm to identify the faulty feeder during single-line-to-ground faults. However, the traditional algorithm might fail to identify the faulty feeder with high impedance faults. With increasing utilization of cable infrastructure, thus increasing the need for resonance grounding, researchers strive to enhance protection. This has led to the QU algorithm, the Directional algorithm, and the CPS algorithm. All utilize transient quantities. But alongside new technologies, the question of efficiency and reliability is raised.
When a single-line-to-ground fault occurs, phase voltages are forced to increase and feeders charge accordingly. By examining the correlation between the zero-sequence voltage and the transient feeder charging process in the zero sequence, the QU algorithm may identify healthy and faulty feeders by their linearity. In contrast, the Directional algorithm evaluates the zero sequence energy flow and the CPS algorithm accumulates multi-frequency admittances obtained by fundamental and harmonic quantities to identify the feeders.
Obtaining quantitative results using numerical simulations and making inductive reasoning by tendencies observed, these dissimilar feeder selection techniques have shown dissimilar tendencies with the variance of fault impedance and feeder characteristics. The feeder selection also differs depending on the over-compensation, cable penetration, and faulty phase, in a system subjected to a high-impedance fault. In fact, with the choice of algorithm, sensitivity differs, misoperation could be avoided, and healthy feeder selections achieved. Regardless, the new algorithms might advance the feeder selection in resonance grounded systems, but none of the new algorithms is superior in its entirety
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Analysis and Testing of Ground Fault Protection Function Performance in Compensated Distribution Grids
No full textDe siste årene har den globale trenden i medium-spennings distribusjonsnett jordet via resonansspole vært å erstatte luftlinjer med underjordiske kabler. Ved å gjøre dette, langsiktige økonomiske og tekniske fordeler kan oppnås. Økende kabellengde i et elektrisk distribusjonsnett medfører en stor økning i kapasitans i det elektriske distribusjonsnettet. Distribusjonsnett i Norge har brukt tradisjonelt, Wattmetriskbasert jordfeilsvern, for å sikre en trygg drift, og oppnå optimal beskyttelse mot enfase jordfeil. Når kapasitansen i et elektrisk distribusjonsnett øker, vil nullsekvensstrømmen i nøytralpunktet av transformatoren bli mer reaktiv, noe som fører til en liten resistiv strøm, som ikke er stor nok for Wattmetriskbasert jordfeildeteksjon og utkobling.
Denne masteravhandlingen tar i bruk Matlab i kombinasjon med Simulink til å etablere et 22 kV, spolejordet distribusjonsnett med to avganger. Relé av typen Siemens SIPROTEC 7UM85 blir brukt til å analysere og teste ytelsen av Wattmetrisk-, Admittans- og Transientbasert jordfeilsfunksjoner. Simulink blir brukt til å undersøke tre ulike tilfeller - en liten Simulink-modell der lengden av begge avgangene er relativt korte blir brukt til å undersøke hvordan variasjon av sensitiviteten til jordfeilsfunksjoner påvirker funksjonenes ytelse. Stor Simulink-modell, der kabellengden av beskyttet avgang blir variert mellom 20 km og 100 km, blir brukt til å undersøke begrensningene av jordfeilsfunksjoner, med tanke på økende kapasitans. Til slutt, blir stor Simulink-modell brukt til å undersøke ytelsen av Wattmetrisk-, Admittans- og Transientbasert jordfeilsfunksjoner når intermitterende jordfeil inntreffer. Det ble opprettet COMTRADE-filer for hver av de ovenfor nevnte tilfellene, og disse ble testet i laboratoriet på det nevnte reléet. Ytelsen av Wattmetrisk-, Admittans-, og Transientbasert jordfeilsfunksjon ble også testet i et eksisterende, norsk distribusjonsnett. Dette ble gjort ved å få tilgang til COMTRADE-filer fra et Norsk nettselskap, og teste disse i laboratoriet.
Analysen og testing av Wattmetrisk-, Admittans- og Transientbasert jordfeilsfunksjonytelse i denne masteravhandlingen har presentert at ved bruk av et simulert distribusjonssystem, kabellengde over 50 km bidrar med nok jordfeilstrøm for å minke ytelsen av Wattmetriskbasert jordfeilsfunksjon. Videre ble det funnet at ved kabellengde 70 km, Wattmetriskbasert jordfeilsfunksjon er ikke lenger i stand til å verken detektere eller koble ut jordfeil med feilresistans over 3 kΩ. Videre blir det vist at ved bruk av en enkel, lang kabel, ytelsen av Transientbasert jordfeilsfunksjon blir både dårlig og inkonsistent. Årsaken til dette ble funnet til å være stor demping grunnet stor nullsekvensresistans. Til slutt, ved bruk av et simulert system, ble det demonstrert at Admittansbasert jordfeilsfunksjon er overlegen sammenlignet med Wattmetrisk- og Transientbasert jordfeilsfunksjon. Det ble demonstrert at for kabellengdene mellom 20 km - 100 km, og for feilresistansene 0 Ω - 4.5 kΩ, Admittansbasert jordfeilsfunksjon har utmerket ytelse. Funnene beskrevet ovenfor ble forsterket ved å teste 38 COMTRADE-filer tilhørende ekte, norsk distribusjonsnett. Det ble demonstrert at ved å teste totalt 38 COMTRADE-filer tilhørende ekte distribusjonsnett, Wattmetrisk-, Admittans- og Transientbasert jordfeilsfunksjon var i stand til å detektere hhv. 68.42%, 94.32% og 81.57% av jordfeilene
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